This invention relates to a subsea deployed line monitoring device for monitoring the integrity of lines, for example electrical cables, used in subsea environments. The invention is particularly applicable to monitoring the integrity of umbilicals, subsea cables and electrical distribution equipment used in controlling, powering and/or monitoring the operation of subsea located equipment such as that used in the extraction of oil or natural gas. However, it may also be used in other applications, such as with equipment used in the off-shore generation of electricity.
Where fluids are extracted from subsea wells it is usual to use control equipment, often located on the sea bed, to control for example, the pumping of fluids to the surface or to control a number of other functions. The control equipment is usually connected to a remote facility, for example at the surface or on land, by way of an umbilical through which electrical power and control signals are routed. The umbilical may also include optical fibres, hydraulic hoses or the like.
Where several control equipment devices are used, as is normally the case, a single umbilical is usually connected between the remote facility and a subsea distribution unit or node, separate cables connecting the distribution unit and the devices to distribute electrical power and control signals there between.
The subsea environment is harsh with respect to electrical circuits of the control equipment devices. When electrical failures occur in the subsea cables and/or connectors it is often difficult to diagnose the cause of the fault, or the fault location.
The most common failure arising from the subsea environment is the failure of insulation as a result of water ingress. Such a failure may result in short circuits between conductors and/or current flow from the live conductor or conductors to earth.
It is common for the umbilical, distribution unit and connecting cables to incorporate a degree of redundancy so that if a fault occurs in one channel of the system, operation can be switched to take that channel out of service.
Usually, surface located equipment is used to monitor the insulation resistance of the umbilical and thereby provide an indication of the status of the umbilical. However, where a transformer or other form of Galvanic isolator is provided, the surface located equipment cannot monitor the insulation resistance or other faults to the other side of the Galvanic isolator.
Some pieces of subsea equipment are provided with line monitoring devices whereby the lines connecting the equipment to, for example, a distribution unit or node, can be monitored. However most subsea equipment currently in use does not have this functionality. Consequently, identification of faults and determination of the location of faults relies heavily on subsea intervention and so is often a time-consuming and expensive process.